Fluxes for use in the treatment of light metals



Patented Mar. 27, 1945 2,372,565 FLUXES For: usem THE TREATMENT OF LIGHT METALS .Edward Frederick Emley, Swinton. Manchester, England, assignor to Magnesium Elektron Limma, London, Britain a England. a companyof Great No-Drawing., Application December 18, 1943', Se-

rial No. 514,840. in 1942 This invention relates to fluxes used for reflning and/or prdtecting against oxidation light metals consisting of magnesium, magnesium base alloys, and aluminium base alloys containing magnesium, all referred to hereinafter as metal. The flux of the presentinvention. is of the inspissated type an example of which is describedinthe specification of British Patent No. 539,024, and which provides a pasty viscous coveror cruston the surface of the molten metal as distinct from the thinlyfluid cover of the fluid type'of flux. The I flux of the said prior patent consists of anhydrous magnesium chloride (SO-50%) chlorides of cal cium, sodium, and potassium, and the 'inspissating agents magnesium oxide and calcium fluoride. The chloridemixture (which I term a "protective base") melts at a low temperature and pro- Great Britain December 24,

aoiaimsfml. 75-93) i I of the calcium'fluoride was avoided and also to 4 obtain satisfactory inspissation of the protective base and a flux of good consistency at all temperatures between 650 C. and 950 C. Thus 'whilst magnesium chloride is usually incor porated in fluxes to increase their fluidity it 'may have just the opposite effect at higher tempe'rature's when used in conjunction with calcium fluoride.

In this way I found it possible to produce sat- 'isfactory fluxes in which the magnesium oxide tects the metal against oxidation during melting.

. Ihave now made investigations with the object of reducing the number of ingredients in the flux with a view to cheapening its production and at the same time if possible to of magnesium chloride, as this is the most expensive constituent. In these investigations I found that in the absence of magnesium oxide (or at any rate less than 5% of magnesium oxide) reducing the quantity the calcium fluoride content requ'ires to be between and 40 per cent to ensure sufficient inspissation and to produce other desirable properties of the flux. With such percentages however it was found that low percentages of magnesium chloride gave unsatisfactory results. The proportion of calcium fluoride required to give. a satisfactory consistency was found to increase rapidly with the temperature which I discovered was due to increasing solubility of the calcium fluoride in the protective base as the temperature increased. Moreover it appeared that calcium fluoride in solution in this manner in the protective base tended to prevent the flux from wetting the molten metal.

Attempts were made by varying the composition of the protective base to reduce its solvent power for calcium fluoride but without success.

After considerable research it was discovered that magnes um tective base even at elevated temperatures and thus as calcium fluoride passes into solution magnesium fluoride is precipitated aslong as magnesium chloride is present in excess. This magnesium fluoride acts as an inspissating agent and it was only necessary to haveproportions of magnesium chloride in the protective base more than stoichiometrically equivalent to the calcium fluoride added to ensure that the non-wetting effect content was less than 5% whilst the magnesium chloride content is fairly low, but suflicient to be equivalent to the calcium fluoride added In fact Ijfound that a slight excess of magnesium chloride over this equivalent was desirable. Thus, whilst 95 parts of magnesium chloride are theoretically equivalent to 78 parts calcium fluoride. I found it desirable to use 95 to 102 parts of magnesium chloride to '78- parts of calcium Nevertheless, whilst itis preferable for themagnesium chloride to be at least stoichiometrically equivalent to the quantity of calcium' fluoride, I flnd that in the case of fairly stiff fluxes the non-wetting tendency due to an insufliciency of magnesium chloride is masked by the viscosity and it is therefore possible to produce satisfactory fluxes containing less magnesium chloride, for example up to 40 percent calcium fluoride with only 40 per cent magnesium chloride. Accordingly the required quantity of magnesium chloride may be regarded as at least equal in weight to'the weight of fluoride.

I also consider thatthe calcium fluoride can be replaced at least partly by another fluoride or other. fluorides of the alkali or alkaline earth in the following ranges of ingredients:

fluoride is insoluble in the pro- Per cent Magnesium ch oride 25 to 48 Alkali oralk ine earth metal fluoride or fluorides -i Over 25 and up to 40. Magnesium oxide Less than 5 Calcium chloride 5 to 27 Sodium chloride Q. Up to 20 Potassium chloride Up to 20 Inert impurities Up to 5 the sodium and potassium chlorides amounting together to between six and thirty per cent, and the magnesium chloride being at least equal in weight to the weight of fluoride or fluorides.

- Per cent Alkali and alkaline earth metal fluoride or fluoaides Over 25 and up to 33 Magnesium chloride 28-39 Calcium hl i v 9-24 Sodium chloride -17 Potassium chloride 3-13 Magnesium oxide Less than 5 Other materials (including oxidic impurities) Less than 5 the sodium and I potassium chlorides together amounting to between 12 and 24% and the magnesium chloride as before being at least equal in weight to the weight of fluoride or fluorides.

As example of specific compositions ofvfluxes that have been tested and found satisfactory the following are cited:

Magnesium chloride V 38 Calcium fluoride 27 81 Magnesium oxide Nil Nil Calcium chloride 17 14 Sodium chloride 13 11 Potassium chloride 8 6 Inert impurities Nil Nil The impurities may comprise barium or strontium chlorides, and oxides such as silica, iron oxide and calcium oxide.

The fluxes were examined for various characteristics including ease of stirring into the inciten metal, stability of the flux cover at high tem- 9,879,668 I peratures, ability to absorb the thinly fluid typo flux used for initial melting of the metal, abilit to absorb magnesium oxide, refining capabilities, hygroscopity, and quantity of flux required. These fluxes were found to be equally as satisfactory as those of British Patent 539,024, whilst the magnesium chloride content has been reduced, Metal was analysed for silicon both before and after treatment with flux of the present invention, and it was found that no appreciable transference of silica from the flux to the metal had occurred.

Iclaim:

l. A flux in which with at least one fluoride selected from the group consisting of alkali and alkaline earth metal fluorides in amount over 25 and up to 40%, and calcium chloridefi to 27% of magnesium chloride 25 to 48%, there is at least one alkali metal chloride in minor amount, and the magnesium chloride being at least equal in weight to the weight of fluoride.

' 2. A flux having a composition within the following range a Per cent At least one fluoride selected from the group consisting of alkali and alkaline earth fluorides Over 25 and up to 33 Magnesium chloride 28-39 Calcium chloride 9-24 Sodium chloride 5-17 Potassium chloride 3-13 Magnesium oxide Less than5 Other materials (including oxidic im- I,

purities) Less than 5 the sodium and potassium chlorides together amounting to between 12 and 24% and the magnesium chloride being at least equal in weight to the weight of fluoride.

3. A flux as claimed in claim 1 wherein calciigm fluoride is the only fluoride in the compos on.

EDWARD FREDERICK EMLEY. 

